As main use of near infrared absorbers is that of recording materials in optical information recording medium. As near infrared absorbers which are used as pigment of recording material, there are known, phenanthrene pigment, naphthoquinone pigment, pyrylium pigment and the like in addition to phthalocyanin pigment and cyanin pigment [see JP-A-55-97033, JP-A-58-83344, JP-A-58-224793, JP-A-58-214162 and JP-A-59-24692]. There are squarylium compounds used for optical information recording medium on which the present applicant has already filed [see JP-A-1-275188 and JP-A-3-188063].
The above described optical information recording media are direct read after write (DRAW) type. However, in addition to those, DRAW type CD has been recently exploited. This type of CD has such the characteristics that a user can record an information therein and the signal after recording can be reproduced by a commercially available CD player since it satisfies with the standards on the previous CD. As recording materials therefor, cyanin pigment and the like are proposed [see JP-A-63-224045, JP-A-2-42652].
However, the above described pigments as recording materials have a variety of problems and therefore optical information recording media using them also have the problems arising from the pigments.
Firstly, the phthalocyanin pigments have the problems that they have extremely low solubility in the organic solvents and can not be used for application by coating. Phenanthrene and naphthoquinone pigments have the problems that they have the lower reflectance in spite of the advantage of easy vacuum deposition. The lower reflectance results in the lower contrast on reflectance between recorded parts by the laser rays and non-recorded parts and therefore the lower reproductivity of the recorded information. Furthermore, the pyrylium and cyanin pigments have the problems that they have the inferior heat resistance and are liable to be deteriorated by the reproducing rays although they can be applied by coating.